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Ring gap formula.

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  • Ring gap formula.

    I am trying to put my perkins engine back together. Is there a formula for the amount of gap the rings should have? Also is there a sequence to the orientation of the rings to each other? I tried to buy a ring insert tool but it looks like in S Africa the mechanics use there fingers as all the shops I tried dont stock them. Also I tried to squeeze the rings on with those cheap spring steel sheet wind up squeezer things and the ring snapped straight away. It is hard to see what is going on when the squeezer is on the piston. Thanks.

  • #2

    Did you try to fit the rings in the bore off the piston? Its easy to check end gap this way. Here is a formula and some charts. see: I never broke rings after they were on the piston with any kind of ring compressor... mostly when I tried to put them on the piston without a ring expander. see: This allows the ring to be enlarged enough to fit it to the piston without stretching it to the breaking point. paul

    Esto Vigilans

    Remember, just because you can doesn't mean you should...
    but you may have to


    • #3
      I usually go by the manufacturers figures, but..

      I've never owned ring pliers and have fitted by hand. The bigest danger is the ring twisting as you spread it and then breaking on the weaker axis. Some shim strips to slide the lower rings over the upper grooves helps. The usual advice is to stagger the ring gaps evenly. I won't assume you've only got three rings and say 120 degrees! Whilst the rings may rotate when running in, I know from evidence from several engines that the rings find a sweet spot and stop.

      I've never had a problem with a ring compressor. Use plenty of oil and make sure there's a slight champher at the top of the bore and no burr.
      Paul Compton


      • #4
        End gap or groove clearance gap? You need both and you need a clean groove. I always clocked the ring gaps in a quarter circle around the wrist pin ends away from the pressure faces on the piston. Did you dry-fit a sample of the rings in a cylinder to see if they fit the hole? Here's a PDF with some end gap info:


        • #5
          Can't help you on the gap...I imagine it's different for diesels than gas engines. Give me an engine model number and I can get the manufacturer's spec if you'd like.

          As far as a ring compressor, in a pinch I've used a hose clamp and some HVAC ductwork sheet metal (28ga I think).


          • #6
            Be wary of a lip at the top of the cylinder, above where the top ring has reached. If the cylinder is worn, the bore will be narrower there.